Boron compound

Boron hydrides heteroboranes, and their metalla derivatives. Commercial aspects. 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

The oxidation of carbon-boron bond converts boranes into alkyl or aryl borates, which may be hydrolyzed subsequently to alcohols and boric acid [991], The oxidation is carried out with hydrogen peroxide [183,1201, 1202] or trimethyiamine oxide [991, 992]. Phenylboronic acids are oxidized to phenols biochemically [1034]. 

A general scheme for the conversion of alkylboranes into alcohols is given in equation 597 [991]. 

The transformation of fributyl borane with trimethyiamine oxide in chloroform into dibutyl boripate is exothermic and rapid at 0 °C, and the transformation of dibutyl botinate into butyl boronate takes place at 25 °C. However, the final conversion of the butyl boronate into tributyl 

To prepare alcohols by the oxidation of alkyl boranes, borane, dibor-ane, alkyl and dialkyl boranes, and dialkoxy boranes are added to alkenes or alkynes. The addition takes place in the anti-Markovnikov mode because boron is more electrophilic than hydrogen. 

Borane, which is used as a complex with tetrahydrofuran [992] or dimethyl sulfide [611, 992] or generated in situ from lithium borohydride with boron trifluoride etherate [646] or sodium borohydride with aluminum chloride [184], reacts with 3 mol of an alkene to form a tertiary borane. The oxidation with alkaline hydrogen peroxide [183, 992, 1201] or with trimethylamine oxide [991, 992] yields an alcohol (equations 598 and 599). 

The electronic structure of the boron atom is 1 s2 2s2 Ip1. It might be expected that boron would lose the outer electrons and be present in compounds as B3+ ions. This ionization, however, requires more than 6700 kJ mol-1, and this amount of energy precludes compounds that are strictly ionic. Polar covalent bonds are much more likely, and the hybridization can be pictured as follows. Promoting a 2s electron to one of the vacant 2p orbitals can be accomplished followed by the hybridization to produce a set of sp2 hybrid orbitals  

The energy necessary to promote the 2s electron to a 2p level is more than compensated for by the additional energy released by forming three equivalent bonds. 

From the above illustration, we expect boron to form three covalent bonds, which are equal in energy and directed 120° from each other. Accordingly, the boron trihalides, BX3, have the following trigonal planar structure (D3h symmetry)  

In fact, all of the compounds containing boron bound to three other atoms have this configuration. In a few cases, such as BFLT and BF4 , sp3 hybrids are formed and the species are tetrahedral (Td symmetry). 

When considering binary compounds of boron, it should be kept in mind that boron does not always behave as if the atom forms compounds in which the octet rule is obeyed. For example, compounds formed with scandium and titanium are ScB2 and TiB2, but other 

Groundwaters, surface waters and drinking water usually contain only low concentrations of compounds which include boron. The range tends to be below 0.01 to 0.1 mg of boron per litre rather than above. Should the 

The boron tolerance of cultivated agricultural plants lies within very 

4 Following extraction of boron with a solution of 2 ethyl-l,3-hexanediol in methyl isobutyl ketone, boron may also be determined in the organic solution by atomic-absorption spectrophotometry 

3 A further proven method of determining boron is that using ICP-AES (see summarized procedure for 24 elements in 3.3.12) 

5 A A Spectrophotometric determination with l,l -dianthrimide General remarks o o 

Various aryl, alkenyl and even alkylborane reagents of different reactivity can be used for coupling with aryl, alkenyl, alkynyl and some alkyl halides, offering very useful synthetic methods. The cross-coupling of aryl and heteroarylboronic acids with aryl and heterocyclic halides and triflates provide useful synthetic routes to various aromatic and heteroaromatic derivatives. Sometimes, the reaction proceeds in the 

The coupling of alkenylboranes with alkenyl halides is particularly useful in the stereoselective synthesis of 1,3-diene systems of four possible double-bond isomers 

The (Z, , )-triene systems in leukotriene and DiHETE were constructed by the coupling of the (ZfT)-dienylborane with the (Z)-alkenyl iodide [129,130]. In the total synthesis of the naturally occurring large molecule palytoxin, which has numerous labile functional groups, Suzuki coupling gives the best results for the creation of the (E,Z)-, 3-diene part (290) by the coupling of the alkenylborane 288 with the (Z)-alkenyl iodide 289. In this case, thallium hydroxide as the base accelerates the reaction 1000 times more than KOH [131]. 

Primary alkylboranes derived by hydroboration of terminal alkenes with 9-BBN-H are coupled with aryl and alkenyl triflates and halides under properly selected conditions. The reaction proceeds smoothly without elimination of /1-hydrogen using PdCTklppf) or Pd(Ph3P)4 and K3PO4 in dioxane or DMF [132]. The intramolecular cross-coupling of the alkenyl triflate with the alkylborane in 292, prepared by in situ hydroboration of the double bond in 291 with 9-BBN-H, is applied to the annulation to 

The important naturally occurring ores of boron are colemanite (Ca gOn 5H20), tincal (Na O 1()H20), and boracite (2Mg3B8015-MgCl2). Boron-containing brines and kernite, or rasorite (Na2B407 4H20), are also sources of boron compounds. 

Crude and refined hydrated sodium borates and hydrous boric acid are produced from kernite and tincal. The ore is fed to the dissolving plant and mixed with hot recycle liquor. Liquor and fine insolubles are fed to a primary thickener. The strong liquors are crystallized in a continuous vacuum crystallizer. 

Another process involves the use of an organic solvent to extract the borax brines. Boric acid is extracted with kerosene, carrying a chelating agent. In a second mixer-settler system, dilute sulfuric acid strips the borates from the chelate. The aqueous phase with boric acid, potassium sulfate, and sodium sulfate is purified by carbon treatment and evaporated in two evaporator-crystallizers. From the first, pure boric acid is separated, and from the other, a mixture of sodium and potassium sulfates. 

Borates, primarily sodium tetraborate, borax (NjB O.,) are used as micronutrients in agriculture. Borax affects the movement of sugars in the plant, sugar carbohydrate equilibrium, protein synthesis, respiration and auxin transport. 

Three borates are used as herbicides sodium metaborate tetrahydrate (Na B O - 4HjO), borate (meta), disodium octaborate tetrahydrate (NUjBgOjj 4HjO), borate (octa) and sodium tetraborate (Na2B O.,) in anhydrous form and as penta-and decahydrate. The name borax refers to the decahydrate form (Anonym, 

At high rates of 1.2-3.5 tons of B20,/ha, all three borates are used pre-and postemergence as total herbicides for soil sterilisation on non-crop sites. At these rates they are suitable also for the eradication of St. John s wort (Litzenberger et al., 1945) and poison ivy (Stodard, 1944). At lower rates of40-100 kg B20j/ha they can also be used for selective weed control in sugar beet and fodder b t (Crafts and Raynor, 1936 Wang and Klotz, 1938 Crafts et al., 1941). 

High doses of borates persist for 2-5 years in the soil, depending on precipitation and the clay content of the soil. Owing to their good solubility in water, borates diffuse into the deeper layers of the soil and can kill deep-rooted weeds. Borates are combined with urea herbicides (e.g. diuron), 2,4-D, chlorates and uracyls. 

In plants treated with borates phytotoxic symptoms develop slowly, the main symptoms being withering and scorching. The biochemical mode of action of borates is unknown. According to the investigations of Brebion et al. (1954), sodium tetraborate considerably inhibits chlorophyll synthesis in young wheat plants, indicating one possible cause of its herbicidal activity. 

Boric acid, B(OH)3 is a very weak acid. It forms the anion [B(OH)4] in 

The content of boron in sewage is gradually increasing due to the increase of the use of washing agents concentrations as high as 5 mg 1 can be found. 

Boron does not represent any health hazard if present at the concentrations occurring in clean surface and fresh groundwaters. However, its presence is not suitable in irrigation waters as it inhibits the growth of plants. Therefore, the concentration of boron in these waters should be limited to values ranging from 0.5-2.0 mg 1  

Perfluorophenyl borate derivatives have also been used as cocatalysts in SPS polymerizations [1]. Various catalyst systems for SPS using borates or boranes were proposed. B(C6F5)3 [1,7], [NR1R2r3h][B(C6F5)4] [8], [NR R R R ] [B(QF5)4] [9], and [Ph3C][B(QF5)4] [10] were used as cocatalysts for the polymerization of styrene. 

In case of borate as cocatalyst, the catalytic activity of the titanium complex with a pentamethylcyclopentadienyl hgand is high, but a titanium complex with a cyclopentadienyl ligand without any substituents is not active for the syndiospecific styrene polymerization. The reason is that the reaction product of the borate and the cycopentadienyltitanium compound is unstable. The stability of the active site with the borate compound is lower in comparison to that with MAO. The reaction of CH2(Cp)2Ti(Me)2 with dimethylanilinium tetrakis(pentafiuorophenyl)borate or tris(pentafluorophenyl)borane in an equimolar mixture has been examined by Miyashita, Nabika, and Suzuki [11]. Two types of methylene bis(cyclopentadienyl)titanium ion complexes were isolated (see Fig. 3.6). These complexes were active in the polymerization of styrene, but only atactic polystyrene was formed. 

Baird et al. [12] examined the catalytic activity of Cp IiMe3 with boranes. The styrene polymer received was a mixture of atactic polystyrene and SPS. Examining the effect of the polarity of the solvent in the polymerization by using CH2CI2 and l,2-C2H4Cl2, it was found that polar solvents increased the yield of the atactic polystyrene. 

TABLE 3.2 Effects of Fluorine of the Borate on Catalytic Activity 

Polymerization conditions styrene, 10ml Cp TiMe3, 5 x ICT mol borate, 5 x l(T mol TIBA, 3 x 10 mol polymerization temperature 70°C time 4h. 

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CHR) , formed, e g. from the reaction of diazomethane and alcohols or hydroxylamine derivatives in the presence of boron compounds or with metal compounds. Poly-methylene is formally the same as polyethene and the properties of the various polymers depend upon the degree of polymerization and the stereochemistry. 

The melting and boiling points of the aluminium halides, in contrast to the boron compounds, are irregular. It might reasonably be expected that aluminium, being a more metallic element than boron, would form an ionic fluoride and indeed the fact that it remains solid until 1564 K. when it sublimes, would tend to confirm this, although it should not be concluded that the fluoride is, therefore, wholly ionic. The crystal structure is such that each aluminium has a coordination number of six, being surrounded by six fluoride ions. 

Volatile boron compounds burn with a green flame. If a solid borate is mixed with methanol and concentrated sulphuric acid, the volatile compound boron trimethoxide, BfOCHj j, is formed and ignition of the alcohol therefore produces a green flame ... 

Ar. Buraq, Pers. Burah) Boron compounds have been known for thousands of years, but the element was not discovered until 1808 by Sir Humphry Davy and by Gay-Lussac and Thenard. 

By far the most commercially important boron compound in terms of dollar sales is Na2B407.5H20. This pentahydrate is used in very large quantities in the manufacture of insulation fiberglass and sodium perborate bleach. 

Boric acid is also an important boron compound with major markets in textile products. Use of borax as a mild antiseptic is minor in terms of dollars and tons. Boron compounds are also extensively used in the manufacture of borosilicate glasses. Other boron compounds show promise in treating arthritis. 

The names of addition compounds are formed by connecting the names of individual compounds by a dash (—) and indicating the numbers of molecules in the name by Arabic numerals separated by the solidus (diagonal slash). All molecules are cited in order of increasing number those having the same number are cited in alphabetic order. However, boron compounds and water are always cited last and in that order. 

Dimethylsulfoxide Acyl and aryl halides, boron compounds, bromomethane, nitrogen dioxide, magnesium perchlorate, periodic acid, silver difluoride, sodium hydride, sulfur trioxide... 

The reaction of adipic acid with ammonia in either Hquid or vapor phase produces adipamide as an intermediate which is subsequentiy dehydrated to adiponitrile. The most widely used catalysts are based on phosphoms-containing compounds, but boron compounds and siHca gel also have been patented for this use (52—56). Vapor-phase processes involve the use of fixed catalyst beds whereas, in Hquid—gas processes, the catalyst is added to the feed. The reaction temperature of the Hquid-phase processes is ca 300°C and most vapor-phase processes mn at 350—400°C. Both operate at atmospheric pressure. Yields of adipic acid to adiponitrile are as high as 95% (57). 

Heating triacetylboron at temperatures above its melting poiat, 123°C, causes a rearrangement to B20(0CCH2)4 (15). An explosive hazard is also generated by dissolving BF ia anhydride (see Boron compounds). 

Other Separations. Other TSA appHcations range from CO2 removal to hydrocarbon separations, and include removal of air poUutants and odors, and purification of streams containing HCl and boron compounds. Because of their high selectivity for CO2 and their abiHty to dry concurrently,... 

Boron. The principal materials used are borax [1303-96-4] sodium pentaborate, sodium tetraborate, partially dehydrated borates, boric acid [10043-35-3] and boron frits. Soil appHcation rates of boron for vegetable crops and alfalfa are usually in the range of 0.5—3 kg/hm. Lower rates are used for more sensitive crops. Both soil and foHar appHcation are practiced but soil appHcations remain effective longer. Boron toxicity is not often observed in field appHcations (see Boron compounds). 

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